During a fault of the utility grid, such as a short circuit or malfunction a wind farm comprising one or more wind turbines may be disconnected from the grid since they cannot supply their active power in a normal energy production state. This kind of disconnection between the utility grid and the wind farm may also be referred to as islanding. In case the wind turbines are disconnected from the utility grid they do not need to be operated in a normal energy production state in which they normally produce energy and supply the produced electric energy to the utility grid. Nevertheless, also in this case of islanding some auxiliary equipment of the wind turbines, such as yaw motors for yawing, control equipment and the like, may require electric energy for operation—due to safety reasons.
In a conventional system a diesel generator may be used to supply electric energy to the auxiliary equipment of the wind turbine.
However, it has been observed that operating the wind turbine in the non-production state, i.e. or for example in the case, where the utility grid is disconnected from the wind turbine, is difficult or causes problems.
There may be a need for a method and for an arrangement for controlling an operation of an electric energy production facility comprising at least one wind turbine during a disconnection in a utility grid, wherein auxiliary equipment of the wind turbine shall be supplied with electric energy in a reliable and cost-effective manner.